1. Field of the Invention
This invention pertains generally to motion sensors, and more particularly to homodyne and other gated or sampling motion sensors based on ultra-wideband (UWB) radar, and most particularly to the receiver in an UWB radar homodyne or other gated or sampling motion sensor.
2. Description of Related Art
Motion detectors, in essence, are evaluated by the success rate of their detection. The reliability of the output of the motion detectors depends largely on the sensitivity of the receiver portion of the motion detectors. Therefore, it is highly desirable to achieve the highest sensitivity at the front-end of the circuit.
Homodyne and impulse motion sensors or detectors based on wideband and ultra-wideband (UWB) radar signals technology have been developed at Lawrence Livermore National Laboratory (LLNL). Both the homodyne and sampling impulse motion sensors include a transmitter and a receiver. In a homodyne system, the transmitter sends out two short bursts of RF per repetition that are separated by a pre-configured distance in time. The second burst will mix with the returned signal from the first transmitted burst. Similarly, in an impulse sampling system, two short pulses separated by a pre-configured distance in time are transmitted per repetition, and the second pulse will mix with the returned signal from the first pulse. If the object in motion is at the distance that corresponds to the separation between the two bursts or pulses, the mixing will create a waveform with the motion artifacts at the output of the receiver at the pulse repetition frequency of the transmitter. Typically, the motion sensors developed at LLNL are homodyne sensors using RF bursts for transmission and reception.
Various techniques exist to down-convert and analyze the incoming RF signal or pulses (the returned signal from the first transmitted RF burst or pulse). How well the selected technique transforms the input signal is one of the parameters that determines the sensitivity of the receivers.
Historically, homodyne motion sensors at LLNL have used a receiver implementation that involves only a single RF detector diode. The nonlinear relationship of voltage and current through the diode allows it to generate nonlinear terms, including the term with no frequency content. With a single diode, however, only the positive or negative half of the waveform coming through the antenna is utilized while the other half is discarded. Therefore, the prior technique limits the sensitivity of detection and leaves room for improvement where the entire waveform is translated to a useful output.
Accordingly it is desirable to provide a receiver architecture that utilizes the entire received RF signal in a homodyne motion sensor.